Totally worthless? Don't know about that. Does a car need a tachometer? No, but I like knowing what's going on engine wise. Same with audio. They will let you know when you're about to "redline" the amp (not the speakers though).
To the OP: Don't know the 6450 that well, but I think it's new enough that it should have a "power guard" or "power sentry" monioring circuit that would take the guess work out of meter calculations.
Above all else, your ears are the best meters. Turn up the volume slowly until you begin to hear stress out of the speakers, note where the meters are and keep it under that level. It doesn't take long to burn out a tweeter or part of a crossover it you go into clipping too long.
To the OP: Don't know the 6450 that well, but I think it's new enough that it should have a "power guard" or "power sentry" monioring circuit that would take the guess work out of meter calculations.
Above all else, your ears are the best meters. Turn up the volume slowly until you begin to hear stress out of the speakers, note where the meters are and keep it under that level. It doesn't take long to burn out a tweeter or part of a crossover it you go into clipping too long.